The present invention relates to aromatic thermoplastic polyester compositions having improved burning characteristics. More particularly, the present invention relates to the employment of tin monoxide in aromatic thermoplastic polyesters to reduce the amount of smoke generated during the burning of the aromatic thermoplastic polyester.
Prior to the present invention, as shown by Japanese patents 7199256 and 7199257, file resistant plastics can be prepared by incorporating a mixture of tin monoxide and antimony trioxide into a halogen containing polyester. The resulting resin self extinguished in 2.5 seconds after it was removed from flame. Although self extinguishing aromatic thermoplastic resins are of significant interest to the plastics industry, it has been found that aromatic thermoplastic polyesters, which are often used in applications such as countertops and window moldings, can generate an unacceptable level of smoke when burned. Total Smoke/M.sup.2 or "TS" is a value recognized by the thermoplastic industry as a measure of smoke performance for a burning thermoplastic.
In order to determine the TS value of a burning thermoplastic, a heat test such as (ASTM-EO96) can be used which is defined as follows:
Polymer plaques (6".times.6".times.1/16") are mounted in the horizontal mode of a test chamber. The environmental test chamber contains a constant flow of air throughout the test. Combustion is initiated by a non-piloted ignition, a piloted ignition of evolved gases, or by point ignition of the surface. If ignited by piloted ignition, the end of the burner tubing is 10 mm above and perpendicular to the exposed horizontal surface of the specimen. Changes in the optical density of gas leaving the chamber are monitored and from this data, smoke release rates are determined. The results for total smoke evolved and smoke release rates are reported in smoke/squared meter of sample and smoke/min/squared meter respectively. The "Smoke" unit is defined by the concentration of smoke particulates in a cubic meter of air that reduces the percent transmission of light through a 1 meter path to 10% as measured by a calibrated photometer. Calculations: Smoke Release Rate=D/kLA(V.sub.o /t) where:
K=absorption coefficient=1.0 squared meter/smoke PA0 D=optical density (absorbance=log (100% T) PA0 L=light path=0.134 m (stack width) PA0 A=exposed surface area of specimen, squared meter PA0 V.sub.o /t=flow rate of air leaving apparatus, cubic meter/min=V.sub.i /t.times.T.sub.o /Ti PA0 V.sub.i /t=flow rate of air entering apparatus, cubic meter/min PA0 T.sub.i,T.sub.o =absolute temperature of air in and out of apparatus respectively.